Traditional acne medications are principally formulated for the teenage market, i.e., products designed for young, oily skin. Teenagers undergoing hormonal changes have skin conditions which are prone to acne break out which is aggravated by oily, sebaceous gland secretions. Current therapies for common acne or "teen acne" are designed to dry oily skin, frequently with harsh solvents such as volatile alcohols. While this may be appropriate for teenage applications, adults and those with sensitive skin conditions such as rosacea find conventional products intolerable. This intolerance manifests itself as a stinging or burning sensation upon application and usually worsens the acne condition being treated.
"Adult acne" has multiple etiologies and mechanisms of pathogenesis which are different from common or teen acne. The major clinical differences include distinctive hormonal patterns which cause changes in the location and type of lesions. In common acne, lesions appear in the perinasal and forehead regions of teenagers, whereas the adult condition usually forms lesions on the chin and neck immediately beneath the mandibles. In teen acne the typical lesion is a comedone otherwise known as a "pimple." Adults tend to form lesions which are primarily inflammatory.
Adult and teen women have different androgen levels which contribute to a variation in oil secretion from the respective skin types. The differences in androgen levels are readily detected by measuring serum content for free dehydro-epiandrosterone sulfate (DHEA-S), luteinizing hormone (LH) and follicle stimulating hormone (FSH). Adult women with acne have relatively elevated androgen levels when compared to female teenagers.
Rosacea is a fairly common dermal condition characterized by sensitive skin which is easily irritated. Starting in the mid to late twenties, increasing telangiectasia (spider veins), inflammatory papules, pustules and nodules develop. In the worst forms, granulomatous inflammatory lesions may result, along with the progressive thickening and coarseness of skin. Rosacea complicated with acne is difficult to treat because of the tendency for hypersensitivity and side effects in this group, particularly when known alcoholic solutions, lotions and gels are applied to an individual's skin.
Irritant folliculitis, caused by epithelial irritations, is another sensitive skin condition which manifests as erythematous papules and follicular pustules. Recurrent episodes of irritant folliculitis are sometimes misdiagnosed as common acne and treated with physical abrasives and exfoliants which traumatize and aggravate the original condition.
The use of salicylic acid in the treatment of common or teen acne is known. For example, U.S. Pat. No. 4,665,063 describes the use of topically applied aspirin (acetyl salicylic acid) for treating common acne; and U.S. Pat. No. 4,891,227 describes the use of pads for applying anti-acne products containing salicylic acid for oily skin. These patents describe state-of-art compositions which emphasize aggressive chemical and physical treatment suitable for teen acne, without addressing the suitability for adult acne and/or the need for mildness.
U.S. Pat. No. 4,800,197 describes a combination of salicylic acid and an anionic taurate surfactant, specifically sodium methyl cocoyl taurate or sodium methyl oleoyl taurate. U.S. Pat. No. 5,296,476 describes the specific use of salicylic acid in combination with calcium citrate. Again, these treatment modalities are designed for aggressive, physical cleansing, which assumes that the individual indicators are normal, young and oily skin.
Currently available forms of salicylic acid tend to aggravate the relatively dry adult acne, and they are particularly unsuitable for those with sensitive skin conditions such as irritant folliculitis. Known salicylic acid preparations are also poorly tolerated in patients suffering from acne complexed with rosacea.
The art also teaches the use of lactic acid for teenage problem skin. See, for example, U.S. Pat. Nos. 3,879,537, 4,234,599, 4,363,815 and 4,380,549 which generally describe the use of alpha-hydroxy acids such as lactic and citric acids for titrating pH in antibiotic preparations. These antibiotic therapies assume that teen acne has predominant etiological ties to opportunistic bacterial infections like those found in acne vulgaris. U.S. Pat. No. 4,507,319 describes the use of lactic acid for adjusting pH in a composition comprising derivatives of 2-hydroxy-octanoic acid or 2-keto-octanoic acid; and U.S. Pat. No. 4,330,531 describes a germ killing composition containing lactic acid which produces chlorine dioxide gas for antibacterial effects on acne vulgaris.
The use of lactic acid derivatives is also known. U.S. Pat. No. 3,806,593 discloses the use of esters of lactic acid; and U.S. Pat. No. 4,540,567 describes the use of lactate esters, preferably ethyl lactate. U.S. Pat. Nos. 4,613,592 and 4,772,592 also refer to lactate esters in compositions which have silicone oil and a C.sub.1 -C.sub.4 alkanol.
Separate uses of salicylic acid and lactic acid in preparations for treating common acne are well known to the relevant art. But, until the present invention, a lactic acid-salicylic acid combination for treating acne of any kind had not been recognized. More significantly, there was no recognition of a lactic acid-salicylic acid combination which is mild and suitable for adult acne and/or sensitive skin compounded with acne.
In fact, the use of lactic acid as an acne medication is discouraged by prior art assays which clinically evaluate sensitive skin by measuring an individual's intolerance to dilute lactic acid solutions. P. Frosch and A. Kligman, A Method for Appraising the Stinging Capacity of Topically Applied Substances, J. Soc. Cosmet. Chem., Vol. 28, pages 197-209 (May 1977).
Based on these considerations, there is a need in the art for a therapeutic dermal composition which is well tolerated by individuals with adult acne and other sensitive skin conditions complicated with acne. To this end, the present invention contemplates at least the following goals.